Пробую вот этот код
document.getElementsByTagName('div.content.thumbnail .item .thumbnail a').innerHTML = '<div class="product-image img-item" style="background-image: url(images.png);"></div>';
добавляю html
<div class="thumbnail"><a href="http://apps.esoftie.com/show_item.php?data=Yz1VUyZsPWVuJmljPUdCJmk9MTcxODM3NTA1MjI1JmE9cyZ4PWF1Y3Rpb25faXRlbXMmdGl0bGU9TEFSR0UgOGNtIFJFQUwgU29mdCBGdXIgQ3JhZnQgQmFsbCBQb20gUG9tIEJvYmJsZSBCYWxsIEZyaW5nZSBCcmFpZCBDaGFybSBUcmltJmltZz1odHRwOi8vaS5lYmF5aW1nLmNvbS9pbWFnZXMvaS8xNzE4Mzc1MDUyMjUtMC0xL3MtbDEwMDAuanBn" target="_blank" onclick=""><div class="product-image img-item" style="background-image: url(images.png);"></div></a></div>